As some of the leading causes of death in the United States, cardiovascular diseases affect millions. Some diseases result in the weakening of blood vessels, while others result from the stenosis of a blood vessel. Stents have been used to provide support and drug-delivery to these blood vessels, but stent implantation carries a number of risks. For example, blood clots may develop at the site of the stent as the body rejects the foreign object, or the stent itself may migrate or fracture. As such, alternative methods of providing support to weakened blood vessels may be desirable.
Another prominent cause of cardiac ischemia and stroke is the occurrence of vulnerable plaque deposits that can accumulate within an individual's vasculature. Such plaque deposits result when a lipid pool forms beneath a thin fibrous cap along the lining of a vessel. When subjected to increased rates of hemodynamic pulsating expansion during systole and elastic contraction during diastole associated with excessive exercise, high mechanical stresses may form in the fibrous cap. Such stresses may lead to rupture of the fibrous cap, releasing a shower of potentially life-threatening emboli into the patient's vasculature. It would therefore be desirable to provide apparatus and methods for isolating and treating vulnerable plaques, so as to minimize the risk of sudden rupture.
A number of solutions have been proposed in the prior art for treating weakened vessels and vulnerable plaques, often involving the placement of a stent within the vessel, with or without a drug-eluting coating. Most stents employ a metal alloy framework, which may include a drug-eluting coating. As noted above, the use of metal stents can introduce additional long-term concerns for patients, including the occurrence of endothelial hyperplasia at the ends of the stent, fatigue fracture and stent migration. More recently, drug-eluting coatings have been employed on some stent designs to reduce the incidence of restenosis, although long-term reduction of restenosis using such coatings has yet to be achieved.
In addition, some previously-known stents have sought to employ naturally occurring biodegradable materials, such as fibrin, or synthetic polymers, such as polyglycolic acid. For example, U.S. Pat. No. 5,510,077 to Dinh et al. describes a stent cast from fibrin by charging a solution of fibrinogen and a fibrinogen-coagulating protein, such as thrombin, in liquid form into a mold cavity containing a metal alloy frame, so as to form a fibrin-coated stent when the fibrin cures. That patent discloses that synthetic polymers, and/or drugs, additionally may be mixed and cross-linked with the fibrinogen and thrombin to improve tissue ingrowth and neointimal formation as the fibrin degrades. However, the patent does not alleviate concerns regarding the fate of the metal alloy frame once the fibrin fully degrades. Moreover, it is believed that such coatings may be relatively fragile, and therefore subject to cracking and delamination resulting from bending and torsional stresses applied to the metal alloy frame in situ.
U.S. Pat. No. 5,591,224 to Schwartz et al. and U.S. Pat. No. 6,312,457 to DiMatteo et al. attempt to overcome the shortcomings of the previously-known devices, such as those described in the Dinh patent, using a support structure formed of elastin, polyglycolic acid or other biodegradable polymer instead of a metal alloy frame. DiMatteo also describes that a fibrin layer on the exterior of the device may be used as an adhesive to adhere the device to the vessel wall. Such materials, however, can be relatively difficult to handle and to deliver within the vasculature using conventional delivery systems, and accordingly no commercially practicable products have been realized using such constructions. Likewise, U.S. Pat. No. 7,399,483 to Stimmeder describes compositions suitable for tissue gluing, sealing or hemostasis, in which a composition of solid fibrinogen and solid thrombin is disposed on a biodegradable carrier, such as a collagen sponge. Such products are not intended for intravascular use and continue to require some form of support structure.
A number of previously known systems have been investigated that could enable an adhesive-coated stent or vascular patch to be delivered intravascularly. For example, U.S. Pat. No. 7,044,982 to Millbocker describes methods of repairing internal defects involving an adhesive-coated prosthetic in which the adhesive is encapsulated within a water soluble material so as to be non-adhesive until the prosthetic is placed in contact with tissue. U.S. Pat. No. 7,402,172 to Chin et al. describes an adhesive-coated intraluminal therapeutic patch having a water soluble coating and a slidable sheath disposed on the delivery catheter to prevent premature activation of the adhesive. To date, the systems described in the foregoing patents do not appear to have overcome the problems inherent in intravascularly delivering an adhesive patch without premature or incomplete activation of the adhesive.